How to Smooth FDM Surfaces

For prototyping plastic parts, fused-deposition modeling (FDM) builds stronger components than any other major additive technology. But the rough, stepped surfaces the technique generates have typically hindered its acceptance for applications that demand smooth finishes like those of production parts. A new smoothing process dubbed Ready Part eliminates this problem, says Product Manager Tim Thellin of Red Eye RPM in Eden Prairie, Minn. (Red Eye is the part-selling arm of Ready Part developer and FDM-machine-builder Stratasys Inc.)

“We use it on ABS components to eliminate stepping and create smooth, mold-quality surfaces,” says Thellin. “First, we build parts with FDM and then remove the support structure. From there, depending on size, one part or group of parts goes through a two-step smoothing process. The first step involves a phase-change reaction between the plastic and an active ingredient.”

It takes only a few minutes to smooth parts, says Thellin. “Because they come out with a nonuniform sheen, we blast them with a substance like baking soda that gives a uniform matte finish,” he says. “The process does not change mechanical properties of the plastic, and parts retain their accuracy and features. Because dimensions don’t change, designers needn’t alter plans to allow for smoothing.

“Another benefit is that ABS parts become sealed for watertight applications,” says Thellin. “And components are smooth enough for painting and plating. Typical lots are from 100 to 4,000. A company might just need 100 parts for a pilot build. Or it might plan to go to hard tooling for injection molding, and use Ready Part in the meantime to get to market faster. We can essentially start running parts the second we get a CAD file over the Internet,” he says.

An ABS white part built with FDM has a smooth, mold-quality surface after undergoing the new smoothing technique.